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Unread 07-29-2015, 12:25 PM   #1
kgb_m3
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Motorcrap 2150 pinging noise unsolved

Been having this issue for 2 years now. Pinging loud under load or up hills. For the longest time I thought it was something mechanical failing and making the noise. I'm 100% sure it's pinging now. My setup is MC2150, TFi ignition upgrade, no computer, all new wiring. We set timing about 9btc, tune the carb for max vacuum and she still pings under load. Retard the timing, it runs like crap, no power.. I'm running stock distributor with Ford cap and rotor, vacuum advance wasn't plugged in, it's now getting full manifold vacuum with little to no luck on pinging.

What are my options at this point? I have a v8 ready to go in, but don't feel like doing the swap just yet. Rather enjoy the jeep with the 4.2 for a few more months if possible but this has to be resolved.

Another piece of info that makes this more confusing. It stops pinging at high altitude. At 4000 feet and higher it goes away.

Thank you for any help in advance!

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Unread 07-29-2015, 01:11 PM   #2
vadslram
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If it is definitely a ping it wouldn't be the fault of the carb, Your timing is too advanced.
Just out of curiosity did you try putting in a tank of premium fuel? If the pinging goes away then you definitely need to pull back the timing a degree or two.
It would stop pinging at high altitude because the air is thinner.

Try the water trick, you might have a carbon build up in the cylinder causing preignition. Get the engine up to operating temp and SLOWLY pour about a cup of water into the carb, If you have a clean squirt spray bottle then use it. Spray as fast as you can into the carb and the water bursting into steam inside the cylinder should knock the carbon buildup off. After you run the water make sure to run the enginge for 10 minutes or so to be sure and dry the system.
Alternately and I'm not an Amsoil paid sponsor, Use the Amsoil Power Foam. Basically it's a foamy Gumout type of stuff and you spray down the carb until the engine stalls, then you let it sit for a few minutes. Then start the engine up and rev it high. You will get billowing clouds out the tail pipe but it does a real good job of cleaning carbon and varnishes off the cylinders.
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Unread 07-29-2015, 02:34 PM   #3
kgb_m3
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Tried putting 91 octane, didn't change a thing. Also retarding the timing just causes either misfire or zero performance. Has to be where it's at for it to run right. Would running older distributor without vacuum advance help any? Maybe it's time to take a 12 gauge to the motor and throw the v8 in. Figured I could get a little more use out of the 4.2 to play in the rocks this summer.
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Unread 07-29-2015, 04:51 PM   #4
dancytron
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Under load going up a hill, the vacuum advance should retarded as much as possible.

It could be that the vacuum advance is so out of adjustment, that it is advancing the vacuum going up hill under a load (i.e. advancing the vacuum even when it is at its lowest). It might also just be gummed up with crap and be sticking.

You can look at the vacuum advance work. Clean it up and make sure it is moving smoothly. It is a little arm on the side of the distributor. You adjust it by putting an 1/8th inch allen wrench into the hole where the vacuum hooks up. Adjust it so that at idle (highest vacuum except when coasting in gear downhill or letting off of the gas from full throttle) it is just at full advance or a tiny bit shy of it. Then it should retard automatically at lower vacuum and MAYBE stop your pinging.

Info on how to do it is buried in this thread. http://www.jeepforum.com/forum/f8/wo...w-tune-973904/
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Unread 07-29-2015, 06:04 PM   #5
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Pinging is detonation. There are only a few reasons for that to happen.
Too much compression and the fuel is firing off from the compressive heat...HIGHLY unlikely in an older 4.2.
Crud buildup in the cylinder that continues to burn like charcoal and igniting the fuel prematurely.
And most probable the ignition firing to soon (advanced) for the situation.

Check to be sure the vac advance is working correctly. The not most accurate but easy way is to get a hand vac pump and run the engine with the advance disconnected. then pump a vacuum to it and see with a timing light what is going on. If it moves ahead it is working at least a little.
I have mine to the manifold vac and it seems to work alright. Most advance when there is the highest vac and therefor the least compression. I've read where others have it the other way, on a ported vacuum where the more airflow over the throttle plate the more advance you get..

Also check your centrifugal advance. that could be off and advancing too far in the high RPM range.
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Unread 07-29-2015, 09:22 PM   #6
kgb_m3
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Ok thanks for the input guys. Here's what we did:

using the 1/8th allen key adjusted the vacuum advance
connected to ported vacuum, went on test drive, didn't really hear pinging
connected to manifold vacuum, went on long test drive, didn't really feel much difference and still didn't hear pinging (maybe very very little if any going up really steep hill)

Timing jumps all over the place, it stays at 9 lets say for 3 seconds, disappears for couple and comes back. Doesn't seem normal. Overall it's running better, but I have a ton of unanswered questions: manifold vs ported vacuum seems to make little to no difference even though they work completely different
if pinging is timing related, then why did it go away completely at high altitude where the only factor that changed was air
theoretically i should be able to tune the carb at sea level without touching timing and get the same results, but doesn't work that way in reality
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Unread 07-29-2015, 09:27 PM   #7
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Let me guess....your EGR has been disabled, or removed.
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Unread 07-29-2015, 11:20 PM   #8
kgb_m3
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Absolutely not, still intact and connected. New charcoal canister, all new vacuum lines, new cat, etc.

I may have wrong weights inside the distributor, if they're not 13r and 18r this could be part of my problem. Tomorrow going to check for top dead center and dizzy placement, make sure all that is on point, check the weights and change spark plugs. Hopefully that takes care of timing jumping around, if not, my chain may be stretched or something else.

Any other ideas?
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Unread 07-30-2015, 12:52 AM   #9
oldRodney
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OK.....

I haven't set the timing on a vehicle in years...[everything is computer controlled nowadays].....
ported vacuum is the proper place to attatch your vacuum advance....
manifold vacuum will raise the timing at idle too much and she will run a little bit faster....

But, as I recall you must pull off the vacuum hose and plug it before you set the timing......

after which, you plug the vacuum back in.....

that is the way I was taught, and practiced doing it that way for years....

if you've already done it this way....then nevermind.......
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Unread 07-30-2015, 12:57 AM   #10
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Back to the egr for a moment. Have you pulled the valve off to check that the passages are clear? All the hot soot in there will crust it shut, or nearly so, and cause pinging.
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Unread 07-30-2015, 01:12 AM   #11
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Quote:
Originally Posted by kgb_m3 View Post
Ok thanks for the input guys. Here's what we did:

**stuff deleted**
if pinging is timing related, then why did it go away completely at high altitude where the only factor that changed was air
theoretically i should be able to tune the carb at sea level without touching timing and get the same results, but doesn't work that way in reality
I'm under the impression that you need to advance the timing when you go to a higher altitude and that the pinging going away at higher altitude indicates that the timing is too advanced at lower altitude.

So it seems to me that adjusting the vacuum advance has fixed it or at least made it better.

As far as the timing jumping around, check to see how much slack is in the timing chain. Search for how. Might need to be replaced.
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Unread 07-30-2015, 01:13 AM   #12
oldRodney
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Here is another thought...

pinging and detonation will occur with a mixture that is too lean....
that is why it all goes away at higher altitude, she is automatically richened up because the air is thinner...
you could try the next size up on your carb jets....
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Unread 07-30-2015, 01:26 AM   #13
oldRodney
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one more thought before I go to bed.....

are you sure you don't have a hellish vacuum leak???

like the carb gasket or intake manifold???

spray a little carb cleaner around and make sure....

good night....
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Unread 07-30-2015, 05:39 AM   #14
vadslram
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Having the timing jump around is NOT good.
Pull the cap and by hand move the crank back and forth to see how much slack you have in the timing chain, There SHOULD be very little even in an old engine.
Also while the cap is off make sure there is no carbon tracking across the posts. It seems wonky that the timing will jump so far as to be off the scale. Could you be getting cross fire from the wires or cap?
Does everything in the centrifigul move smoothly?
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Unread 07-30-2015, 07:32 AM   #15
Mike Romain
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The timing advance plate has a wick under the rotor that is supposed to get a few drops of oil every tune up to keep it moving. Your symptoms imply it might be sticky. I have had to dissemble several to free them up.
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